1931 ] 
Notes on the Genus Ephemerella 
33 
toward the tips of the tails, which appear practically hair- 
less. 
Nymph: (light variety) . 
(Taken in Cascadilla Creek, Salmon Creek, Otter Creek, 
Van Buskirk’s Glen, North Harford Brook, and North 
Spencer Stream.) 
Measurements : body 10 mm., tails 6 mm. Head and body 
rounded and smooth. Posterior angles of head indrawn. 
Labium not marked with grayish as in the dark variety. 
General color light brown, tibia and tarsus banded with 
light brown. Front angles of the prothorax only slightly 
rounded, lateral margins only slightly flaring. Dorsal spines 
present on segments 4-9, but not so well developed as in 
the dark variety. Sometimes very slight spines can be 
detected on segments 2 and 3. Gills present on segments 
3-7, the 7th gill not being so completely covered by the 6th 
as in the dark variety. 
I do not feel that these two are different species, but 
regard them merely as color varieties of E. rotunda. The 
differences seem to be a matter of degree, with intergrada- 
tions of such characters as the prominence of the dorsal 
spines, the extent to which the 6th gill covers the 7th, the 
toothing of the prothorax and metathorax, and the flaring 
of the lateral prothoracic margins. This species seems to 
exhibit many variations in color — from the very dark 
variety described above, to a light yellow variety with dark 
markings whose essential characters are the same. 
E. rotunda was the most common and abundant member 
of the genus in the Ithaca streams from early March until 
late May. It was the earliest nymph collected, being found 
in great numbers and fully matured as early as March 16th. 
The last nymphs were seen in the North Harford Brook on 
June 11th. Although Miss Morgan and several others had 
never found the males of E. rotunda, I was able both to 
collect and to rear many. I did not notice any; particular 
scarcity of males, the sexes being fairly equally distributed 
where the nymphs were obtainable at all. The male adults 
